The present invention relates to an image recording apparatus in which a recording material is pressurized and conveyed, and more particularly to an image recording apparatus in which a recording material is pressurized with rollers in such a manner that the image is fixed on the image receiving sheet.
An example of an image recording material which requires pressurization is disclosed in Japanese Unexamined Patent Application No. 179836/1982. In this image recording material, synthetic macromolecular resin wall capsules containing a vinyl compound, photopolymerization initiator and color agent precursor are supported on a support. In an image recording method using the image recording material, upon exposure, the microcapsules are hardened according to the image, and the remaining, unhardened microcapsules are broken by the application of pressure thereto so that the coloring agent precursor is discharge to form a colored image.
The method is advantageous in that images high in quality can be readily obtained by dry processing; however, it is disadvantageous in that the image recording material has a much lower photosensitivity than one using a silver halogenide.
The present applicant has disclosed a novel image recording material in Japanese Patent Application No. 117089/1985 which has a sufficiently high photosensitivity and can provide an image of high quality by simple dry processing. The image recording material is formed by coating a support with at least photosensitive silver halogenide, a reducing agent, a polymerizing compound and a color image forming material, wherein at least the polymerizing compound and the color image forming material are photosensitive compounds sealed, in combination, in microcapsules.
An image recording method using this photosensitive material is disclosed in Japanese Patent Application No. 121284/1985, also filed by the present applicant. In such an image recording method, the image recording material is exposed to form a latent image thereon, and the latent image is developed by heating so that the polymerizing compound in the latent image is polymerized to produce a macromolecular compound, thereby to harden the microcapsules. After development, the image recording material is laid on an image receiving material onto which the color image forming material can be transferred. The image recording material and the image receiving material are pressurized so that at least some of the microcapsules in the regions where no latent image is formed are broken. As a result, the color image forming material is transferred to the image receiving material to form a color image thereon.
On the other hand, an automatic image recording apparatus has been proposed in the art in which a latent image formed on photosensitive material as described above is developed by heating, the photosensitive material is laid on the image receiving material, and the photosensitive material and the image receiving material are pressurized so that the image is transferred onto the image receiving material with the desired color density.
In this automatic image recording apparatus, the developed image is transferred from the photosensitive material onto the image receiving material as follows. The photosensitive material and the image receiving material, after being laid one on another, are inserted into a pair of pressurizing nip rollers so that a high pressure of 500 kg/cm.sup.2, for instance, is applied thereto from both sides.
However, since the pressurizing nip rollers are supported at their opposite ends, the pressures produced at the two ends of the rollers are higher than that produced at the middle; that is, the pressurizing nip rollers provide different pressures at different positions, with the result that the image is not uniformly transferred onto the image receiving sheet.
The image recording material is pressurized with such rollers for fixing the image not only in the above-described image recording device but also in an electrophotographic device. In the latter case also, the high pressure applied to the image recording material is unavoidably not uniform.
For the purpose of solving the above-described problems, for instance, a skew roller type pressurizing device and a back-up roller type pressurizing device have been proposed in the art. In the skew roller type pressurizing device, a pair of pressurizing nip rollers are arranged in such a manner that they form a relatively small nip so that the pressure applied to the nip region of the two rollers is uniform over the entire length thereof. In the back-up roller type pressurizing device, back-up rollers are arranged on both dies of a pair of pressurizing nip rollers arranged in parallel with each other so that the pressure applied to the nip region of the pressuring nip rollers is made substantially uniform over the entire length thereof.
However, the skew roller type pressurizing device is disadvantageous in that it cannot be used with image recording materials differing in thickness and/or width. Furthermore, when a photosensitive material and an image receiving material stacked together is conveyed while being pressurized, they have a tendency to shift from each other more at the rear end portion than their front end portion because they are conveyed in directions perpendicular to the axes of the respective nip rollers with which they are in contact.
The back-up roller type pressurizing device also suffers from a difficulty in that, as it needs two back-up rollers in addition to the pressurizing nip rollers, the device is unavoidably bulky and increased in weight.
In addition, in both these pressurizing devices, it is essential to precisely adjust the pressures of the pressurizing nip rollers, with the result that the mechanism is intricate and difficult to maintain.